Abstract
It is now apparent that the activities of many bacterial genes are regulated by several interlocking control apparatuses that respond to different small molecule effectors. An overview suggests the existence of a hierarchy of controls (Zubay, 1973). For example, the gene cluster known as the lac operon is induced by the presence of lactose. Lactose is also the substrate of the enzyme β-galactosidase, which is encoded by the lac operon. The induction of the lac operon by lactose is brought about by a highly specific control process that does not directly affect the activities of other genes. At a more general level of control, the expression of the lac operon is dependent upon the presence of 3’:5’-cyclic AMP (cAMP). This dependence is characteristic of many genes that encode catabolic enzymes. At an even more general level of control, we find a mechanism that appears to modulate transcription according to the gross rate of translation. The small molecule effector for this control process is probably guanosine tetraphosphate (guano-sine bis-diphosphate, ppGpp). The effect this compound has depends upon the gene — for the lac operon ppGpp is stimulatory.
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Zubay, G., Yang, HL., Reiness, G., Cashel, M. (1973). Regulation of Bacterial Genes. In: Hamkalo, B.A., Papaconstantinou, J. (eds) Molecular Cytogenetics. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-7479-8_20
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DOI: https://doi.org/10.1007/978-1-4615-7479-8_20
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